The teargas used by interior ministry troops in Cairo's Tahrir Square
is supplied by a US company. Demonstrators say cartridges retrieved
from the scene are branded with the name and address of Combined Systems
Inc (CSI).

The
firm is located in Jamestown, Pennsylvania. It specialises in supplying
what it calls "crowd control devices" to armies and "homeland security
agencies" around the world. It also manufactures lethal military
equipment.

Protesters say the CS gas seems more powerful than that
used by Egyptian police during the country's last popular uprising in
February. "It's stronger, it burns your face, it makes you feel like
your whole body is seizing up," one witness said. He added: "It doesn't
seem to be combated by Coke or vinegar."

Experts told the Guardian the gas was likely to be standard CS gas, but the effects could be exacerbated by physical exertion.

As
well as the effects of the teargas, protesters have suffered grave
injuries to their heads and faces from rubber bullets. There are also
reports of live ammunition being used. Dozens of people have been taken
to makeshift hospitals after inhaling the choking gas fired by the
Central Security Forces.